Laser pulses with energy of ~10 μJ are generated at 46.9 nm on the 3p-3s transition of the Ne-like Ar by a fast capillary discharge setup in both 3- and 4-mm channels. The dependence of the laser output pulse energy on the pressure of Ar gas is measured for 3-mm-diameter capillaries at currents of 25, 30, and 35 kA. Under the same discharge conditions used in 3-mm capillaries, experiments indicate that higher and faster current pulses are required to produce soft X-ray amplification in 4-mm-diamater capillaries.